The understanding of gene expression has been greatly enhanced by the ability to transfer cloned genes into cells and to study the mechanism of their regulation. For the past several years it has been recognized that retroviruses are good candidates as vehicles or vectors to introduce genes into eucaryotic cells. Retro-virus-derived vectors utilize the biochemical processes unique to this group of viruses to transfer genes with high efficiency into a wide variety of cell types in vitro and in vivo. By using retrovirus-derived vectors, the effect of newly introduced genes and the mechanism of gene expression can be studied in cell types, so far refractory, to other methods of gene transfer. The special features of this new gene transfer technology have provided for the first time the opportunity of introducing genes into the somatic cells of live animals. Although at present, gene transfer technology is mainly limited to gene transfer into hemopoietic cells, its potential in general studies and applications to human therapy is beginning to be recognized.
As with many new emerging technologies, the potential of retroviral gene transfer created great expectations. It was quickly realized that retroviral gene transfer is not a simple technique to adapt, and the initial euphoria gave vent to overt pessimism. Recent progress in this field is encouraging, and there is perhaps reason for cautious optimism that some of the expectation generated by this new gene transfer technique will be fulfilled.